Transient Heating Burner and Method

ABSTRACT

A transient heating burner including at least two burner elements each including a distribution nozzle configured to flow a first fluid and an annular nozzle surrounding the distribution nozzle and configured to flow a second fluid, the burner also including a controller programmed to independently control the flow of the first fluid to each distribution nozzle such that at least one of the distribution nozzles is active and at least one of the distribution nozzles is passive, wherein flow in an active distribution nozzle is greater than an average flow to the distribution nozzles and flow in a passive distribution nozzle is less than the average flow to the distribution nozzles, wherein the first fluid contains a reactant that is one of fuel and oxidant and the second fluid contains a reactant that is the other of fuel and oxidant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the priority of, U.S.application Ser. No. 14/193,698 filed on Feb. 28, 2014, which isincorporated by reference herein in its entirety.

BACKGROUND

This application relates to a burner and method for heating a furnace,and in particular an industrial melting furnace, to provide enhancedheat transfer while improving uniformity of heating and reducingpotential overheating and oxidizing conditions at a melt bath surface.

In a conventional system, the heat, provided by a stationary flame, isnot directed towards the melt, thereby limiting the heat transfer fromthe flame to the melt. Moreover, if a conventional system were modifiedto direct a stationary flame toward the melt, undesirable overheatingand oxidation of the metal may occur. An approach to avoid overheating,as taught in U.S. Pat. No. 5,554,022, is to direct a low momentum flametoward the melt and then impinge of high momentum jet onto the lowmomentum flame, causing the flame to move. However, in this approachthere is still a significant potential for metal oxidation and buoyantflames that can interact with and overheat the furnace refractory.

SUMMARY

A transient heating burner and method provide enhanced flame coverageand view factors in a furnace. The configuration of the burner enablesoptimum heat flux delivery both spatially and temporally so that auniform temperature distribution can be achieved and maintained in afurnace. Uniform heat flux is achieved by directing the heat flux toappropriate locations, for example as determined by an algorithm, basedon furnace geometry, or based on real-time feedback from one or moresensors, for certain amounts of time. The burner and method enableselectively longer and more penetrating flames that can impinge thecharge in a furnace to provide improved melting, while minimizingoxidative melt losses. In particular, multiple high momentum flames aredirected towards the melt in a cyclical manner. Overheating is avoidedand energy is distributed more evenly over the melt bath. The burner isalso capable of generating vortices by selectively modulating multipleflames. In particular, the burner has a plurality of separate burnerelements, each with its own flame in a passive or active state, that canbe modulated in various patterns and frequencies to achieve the desiredheat flux profile.

Various embodiments of a transient heating burner are described. Theburner includes at least two burner elements each having a distributionnozzle configured to flow a fuel and an annular nozzle surrounding thedistribution nozzle and configured to flow a first oxidant, and at leastone staging nozzle configured to flow a second oxidant. A controller isprogrammed to independently control the fuel flow to each distributionnozzle and to control a staging ratio to be less than or equal to about75%. The controller controls flow so that at least one of thedistribution nozzles is active and at least one of the distributionnozzles is passive, wherein fuel flow in an active distribution nozzleis greater than an average fuel flow to the distribution nozzles andfuel flow in a passive distribution nozzle is less than the average fuelflow to the distribution nozzles.

The staging ratio is the ratio of the oxygen contained in the secondoxidant flow to the sum of the oxygen contained in the first and secondoxidant flows.

The burner elements may be spaced substantially evenly apart in acircumscribed circle, and the staging nozzle is positioned within thecircumscribed circle. In one aspect, the burner includes three burnerelements each spaced 120° apart from adjacent burner elements. Inanother aspect, the burner includes four burner elements each spaced 90°apart from adjacent burner elements. In further aspects, the burner mayinclude five or six burner elements spaced evenly around a circumscribedcircle.

In one aspect, at least one of the burner elements is angled radiallyoutward at an angle α from the circumscribed circle. The burner elementsmay all be angled at the same angle α, or each burner element, n, may beangled radially outward at a different angle α_(n). The angle α ispreferably less than or equal to about 60° and more preferably fromabout 10° to about 40°.

In another aspect, at least one of the burner elements is angledtangentially at an angle β with respect to the circumscribed circle. Theangle β is preferably less than or equal to about 60°, and morepreferably from about 10° to about 40°.

In another embodiment of a burner, the burner elements and the stagingnozzle are positioned generally collinearly with each staging nozzlelocated approximately equidistant between two burner elements. In oneaspect, the burner has at least three staging nozzles, including acentral staging nozzle, and at least four burner elements positionedalternately with the staging nozzles. In another aspect, the burnerelements and the staging nozzles on either side of the central stagingnozzle are angled at an angle γ away from the central staging nozzle.

In another embodiment of a burner, the distribution nozzles and annularnozzles of the burner elements each have a cross-section with a minoraxis and a major axis at least 1.5 times as long as the minor axis. Atleast two staging nozzles are positioned generally collinearly andsubstantially parallel to the major axes, and are adjacent to eachburner element.

In another embodiment of a burner, the staging nozzle has across-section with a minor axis and a major axis at least 1.5 times aslong as the minor axis, and at least two burner elements are positionedcollinearly, and are adjacent to the staging nozzle and substantiallyparallel to the major axis. In one aspect, the burner elements areangled outward from the minor axis of the staging nozzle at an angle Φof less than about 45°.

The controller is programmed to control fuel flow to a passivedistribution nozzle to be greater than zero and less than or equal tohalf the flow rate of an active distribution nozzle. In one embodiment,the controller is programmed to control the staging ratio to be lessthan or equal to about 40%.

In another embodiment, the fuel exiting an active distribution nozzlehas an active jet velocity and oxidant exiting the staging nozzle has astaging jet velocity, and the controller is programmed to control theratio of the staging jet velocity to the active jet velocity to be atleast about 0.05 and less than 1. Preferably, the ratio of the stagingjet velocity to the active jet velocity is controlled to be from about0.1 to about 0.4.

In one aspect, the first oxidant flowing through the annular nozzles hasan oxygen concentration of equal to or greater than about 70%. Inanother aspect, the second oxidant flowing through the staging nozzlehas an oxygen concentration of equal to or greater than about 20.9%.

In another aspect, an active distribution nozzle has an active jet flowrate and wherein a passive distribution nozzle has a passive jet flowrate, and the controller is programmed to control the ratio of theactive jet flow rate to the passive jet flow rate to be from about 5 toabout 40. Preferably, the controller is programmed to control the ratioof the active jet flow rate to the passive jet flow rate to be fromabout 15 to about 25.

In another aspect, a burner element having a passive distribution nozzlehas an equivalence ratio from about 0.2 to about 1. In another aspect, aburner element having an active distribution nozzle has an equivalenceratio of from about 1 to about 10. The equivalence ratio is the ratio oftheoretical stoichiometric oxidant flow through the annular nozzle toactual oxidant flow through the annular nozzle to combust the fuelflowing through the distribution nozzle.

In another embodiment, a sensor is configured to provide a signal to thecontroller. The controller is programmed to control each distributionnozzle to be active or passive based on the signal. The sensor isselected from the group consisting of temperature sensors, radiationsensors, optical sensors, cameras, color sensors, conductivity sensors,proximity sensors, and combinations thereof.

In one embodiment, the first oxidant and the second oxidant have thesame oxygen concentration. In another embodiment, the first oxidant andthe second oxidant have different oxygen concentrations.

In one embodiment, the staging nozzle includes a swirl vane to impartswirl to the second oxidant.

A method of operating a burner in a furnace is described, the burnerhaving at least one staging nozzle and at least two burner elements eachcomprising a distribution nozzle surrounded by an annular nozzle. Themethod includes flowing oxidant at a staging flow rate through thestaging nozzle, flowing oxidant at a primary oxidant flow rate througheach of the annular nozzles, selecting at least one of the distributionnozzles to be active and at least one of the distribution nozzles to bepassive, flowing fuel at an active jet flow rate through the activedistribution nozzles, and flowing fuel at a passive jet flow ratethrough the passive distribution nozzles, wherein the active jet flowrate is greater than an average fuel flow rate through the distributionnozzles and the passive jet flow rate is less than the average fuel flowrate through the distribution nozzles.

The method may further include sensing a parameter in the furnace,reselecting which distribution nozzles are active and which distributionnozzles are passive based on the sensed parameter, and periodicallyrepeating the sensing and reselecting steps.

An embodiment of a transient heating burner is described. The burnerincludes at least two burner elements each having a distribution nozzleconfigured to flow a first fluid, an annular nozzle surrounding thedistribution nozzle and configured to flow a second fluid, and at leastone staging nozzle configured to flow a third fluid. The burner furtherincludes a controller programmed to independently control the flow ofthe first fluid to each distribution nozzle such that at least one ofthe distribution nozzles is active and at least one of the distributionnozzles is passive, and to control a staging ratio to be less than orequal to about 75%. Flow in an active distribution nozzle is greaterthan an average flow to the distribution nozzles and flow in a passivedistribution nozzle is less than the average flow to the distributionnozzles. The staging ratio is the ratio of the third fluid flow to thesum of the second fluid flow and the third fluid flow. In thisembodiment, the first fluid contains one of fuel and oxygen and thesecond fluid and the third fluid contain the other of fuel and oxygen,wherein the fuel and oxygen are reactants.

Other aspects of the invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end perspective view of an embodiment of a transientheating burner.

FIG. 2 is a control schematic for an embodiment of a transient heatingburner.

FIG. 3 is an operational sequence schematic for an embodiment of atransient heating burner as in FIG. 1.

FIGS. 4A and 4B are an end view schematics showing nozzle orientationsfor two embodiments of a transient heating burner.

FIGS. 5A-5E are end views of various embodiments of a transient heatingburner. FIG. 5A shows a burner having a central staging nozzlesurrounded by four burner elements angled radially outward; FIG. 5Bshows a burner having a central staging nozzle surrounded by four burnerelements angled tangentially along a circumscribed circle; FIG. 5C showsa burner having a collinear arrangement of alternating burner elementsand staging nozzles in which all but the central staging nozzle areangled outward; FIG. 5D shows a burner having four collinear burnerelements adjacent to and substantially parallel to the major axis of aslotted staging nozzle; and

FIG. 5E shows a pair of aligned flat flame burner elements and a pair ofcollinear staging nozzles adjacent to and substantially parallel to themajor axis of each burner element.

FIGS. 6A-6D show various possible geometries of a distribution nozzlewithin each burner element.

FIG. 7 is a perspective view of a furnace showing two possible mountingorientations of a transient heating burner.

FIG. 8 is a graph comparing on a relative scale NOx production data froma conventional oxy-fuel burner, a conventional staged oxy-fuel burner,and a transient heating burner, in both luminous and non-luminous modes.

DETAILED DESCRIPTION

FIG. 1 depicts one embodiment of a transient heating burner 10. Theburner 10 includes a body 12 having a face 14, wherein when the burner10 is mounted in a furnace (for example as in FIG. 7), the face 14 isexposed to the combustion zone in the furnace.

The burner 10 includes a plurality of burner elements 20 oriented so asto define a circumscribed circle (see FIG. 4A), with the burner elements20 preferably equally spaced around the circumscribed circle. At leastone staging nozzle 30 is positioned within the circumscribed circle. Forreference purposes, an active jet (A) and a passive jet (P) aredepicted, to show that the active jet has a larger flame than thepassive jet.

The burner 10 depicted in FIG. 1 has four burner elements 20 spacedapart at approximately 90° intervals. However, it is understood that theburner 10 may include any number n of burner elements 20 equal to orgreater than two. For example, a burner 10 may have two burner elements20 spaced so as to be diametrically opposed, or alternately three burnerelements 20 spaced apart at approximately 120° intervals, or five ormore burner elements 20 spaced apart at approximately even intervals. Itis also understood that for some furnace geometries, configurations, oroperating conditions, it may be desirable to have a burner 10 with aplurality of burner elements 20 that are unequally spaced apart aroundthe circumscribed circle. In a further alternative, the burner 10 mayhave a plurality of burner elements 20 that are positioned to define ageometric shape other than a circle, for example an oval or an irregularpolygon, depending on the furnace geometry and configuration.

The burner 10 in FIG. 1 has one centrally positioned staging nozzle 30.However, it is understood that a plurality of staging nozzle 30 may beprovided, wherein the staging nozzles 30 may be all of the same size orof different sizes. Additionally, depending on furnace geometry, desiredflame characteristics, the orientation of the individual burner elements20, and other factors, the staging nozzle(s) 30 may be positioned offcenter within the circumscribed circle defined by the burner elements20. The staging nozzle 30 may be of any shape.

Each burner element 20 includes a distribution nozzle 22 surrounded byan annular nozzle 24. A distributed reactant is flowed through thedistribution nozzle 22 while a staged reactant is flowed through theannular nozzle 24, wherein one reactant is a fuel and the other reactantis an oxidant. A portion of the staged reactant is also flowed throughthe staging nozzle 30. In one embodiment, fuel is flowed through thedistribution nozzle 22 as the distributed reactant, while oxidant isflowed through the annular nozzle 24 as the staged reactant. In anotherembodiment, oxidant is the distributed reactant flowed through thedistribution nozzle 22 and fuel is the staged reactant flowed throughthe annular nozzle 24. The proportion of staged reactant introducedthrough the annular nozzles 24 as compared with the staging nozzle 30can be adjusted in order to maintain stable burner operation and/or tocontrol flame properties such as heat release profile.

As used herein, the term “fuel” denotes any hydrocarbon-containingsubstance that can be used as fuel in a combustion reaction. Preferably,the fuel is a gaseous fuel, such as natural gas, but the fuel may alsobe an atomized liquid fuel or a pulverized solid fuel in a carrier gas.As used herein, the term “oxidant” denotes any oxygen-containingsubstance that can oxidize fuel in a combustion reaction. An oxidant maybe air, vitiated air (i.e., gas with less than about 20.9% oxygen),oxygen-enriched air (i.e., gas with greater than about 20.9% oxygen), oressentially pure oxygen (i.e., gas with approximately 100% oxygen). Inpreferred embodiments, the oxidant is an oxygen-enriched air having anoxygen concentration of at least about 26%, at least about 40%, at leastabout 70%, or at least about 98%.

The distribution nozzle 22 can be of any shape. A subset of possibleexemplary shapes is shown in FIGS. 6A-6D, including a slotted nozzle(FIG. 6A), a single-slot nozzle (FIG. 6B), a circular nozzle (FIG. 6C),and a multi-hole nozzle (FIG. 6D). A more detailed discussion ofpossible nozzle shapes can be found in U.S. Pat. No. 6,866,503,incorporated herein by reference in its entirety. For example, to createa luminous flame with high radiative transfer properties, a distributionnozzle 22 having a shape factor of less than 10 can be used, while tocreate a non-luminous flame which may have lower NOx, a distributionnozzle having a shape factor of 10 or greater can be used. Luminous modemight be preferred for melting operations, while non-luminous mode mightbe preferred for reheating operations. Note that a high shape factornozzle can include a multi-hole nozzle. As described in detail in U.S.Pat. No. 6,866,503, the shape factor, σ, is defined the square of theperimeter, P, divided by twice the cross-sectional area, A, or inequation terms:

α=P ²/2A.

FIG. 2 shows a simplified control schematic for a burner 10 as describedabove. A first fluid F1 is supplied to the distribution nozzles 22 at atotal flow rate controlled by a control valve 23. The flow of the firstfluid F1 to each distribution nozzle 22 is separately controlled. In oneembodiment, a control valve 26 upstream of each distribution nozzle 22is modulated between a high flow and a low flow position, correspondingrespectively to an active state and a passive state for the burnerelement 20 containing that distribution nozzle 22. In an alternateembodiment, the control valve 26 is positioned in parallel with a bypasspassage 27. In this embodiment, the control valve 26 is modulatedbetween an open position and a closed position, again correspondingrespectively to active and passive states of the burner element 20,while the bypass passage 27 allows a relatively small amount of flow tobypass the control valve 26 so that some of the first fluid F1 is alwaysflowing to the distribution nozzle 22, even in the passive state.

The effect of either arrangement is to modulate the flow through thedistribution nozzle 22 between an relatively higher active flow rate anda relatively lower passive flow rate. For example, an active flow ratemay be defined as a flow rate greater than an average flow rate to thedistribution nozzles 22, while a passive flow rate may be defined as aflow rate less than the average flow rate to the distribution nozzles22. The average flow rate is determined by dividing the total flow rateof the first fluid F1 by the total number n of distribution nozzles22/burner elements 20. Other relationships between the active flow rateand the passive flow rate may be used, with the active flow rate alwaysbeing greater than the passive flow rate.

Regardless how the active and passive flow rates are determined, thepassive flow rate must be greater than zero flow. The passive flow rateis sufficient to maintain combustion in each burner element 20, so as toprovide a mechanism for immediate ignition when a burner element 20 isswitched from the passive state to the active state. The non-zeropassive flow rate also protects the distribution nozzle 22 from entry offoreign materials. In one embodiment, the passive flow rate is less thanor equal to half of the active flow rate. In another embodiment, theratio of the active flow rate to the passive flow rate is at least about5 and no greater than about 40. In yet another embodiment, the ratio ofthe active flow rate to the passive flow rate is at least about 15 andno greater than about 25.

A second fluid F2 is supplied to the annular nozzles 24. A control valve28 controls the total flow rate of the second fluid F2 to the annularnozzles 24, and a manifold 29 distributes the flow approximately equallyacross the n annular nozzles 24. A third fluid F3 is supplied to thestaging nozzle 30, and the flow rate of the third fluid F3 is controlledby a control valve 32. The staging nozzle 30 may include a swirl vane orother mechanism (not shown) to impart swirl to the third fluid F3exiting the staging nozzle 30. Swirl imparted on the third fluid F3 willresult in break-up of that fluid jet, which can aid in entrainment ofthe third fluid F3 jet by the active jet(s). However, intense swirl isnot desirable since it could dominate the flow structure and alter flameshapes.

The second fluid F2 and the third fluid F3 contain the same type ofreactant, either fuel or oxidant. For example, when the first fluid F1is fuel, the second fluid F2 and the third fluid F3 are each oxidants,and when the first fluid F1 is oxidant, the second fluid F2 and thethird fluid F3 are each fuels. In one embodiment, the second fluid F2and the third fluid F3 are different fluids, i.e., each has the samereactant (fuel or oxidant) but in different concentrations. In thiscase, the control valve 28 and the control valve 32 must be separatevalves to control the two fluids F2 and F3. In an alternate embodiment(not shown), when the second fluid F2 and the third fluid F3 are thesame fluid having the same concentration of the same reactant, a stagingvalve can be used in place of the control valve 28 and the control valve32 to distribute a portion of the flow approximately equally to the nannular nozzles 24 and the remainder of the flow to the staging nozzle30.

In the depicted embodiment, the flow rate of the second fluid F2 to eachof the annular nozzles 24 is not controlled independently. As a result,each annular nozzle 24 always flows about an average flow rate of thesecond fluid F2 when the control valve 28 is open. The average flow rateis determined by dividing the total flow rate of the second fluid F2 bythe total number n of annular nozzles 24/burner elements 20.Alternatively, the flow rate of the second fluid F2 to each annularnozzle 24 may be independently controlled.

In the depicted embodiment, because the flow rate of the second fluid F2to each annular nozzle 24 is about the same, each burner element 20operates on either side of stoichiometric depending on whether thatburner element 20 is active or passive at the time. When a burnerelement 20 is in the active state, that burner element 20 operates offof stoichiometric, and sometimes well off of stoichiometric, in onedirection, and when the burner element 20 is in the passive state, thatburner element 20 operates off of stoichiometric, and sometimes well offof stoichiometric, in the opposite direction. For example, when thefirst fluid F1 is fuel and the second fluid F2 is oxidant, a burnerelement 20 in the active state will operate fuel-rich and a burnerelement 20 in the passive state will operate fuel-lean. Alternatively,when the first fluid F1 is oxidant and the second fluid F2 is fuel, aburner element 20 in the active state will operate fuel-lean and aburner element 20 in the passive state will operate fuel-rich. However,because the total flow of fuel and oxidant is controlled by controlvalves 23 and 28 (and also by a staging control valve 32), the overallstoichiometry of the burner 10 remains the same regardless which, andhow many, burner elements 20 are in the active state versus the passivestate.

The stoichiometry at which each burner element 20 operates may becharacterized by an equivalence ratio. For a given fuel flow rate, theequivalence ratio is determined as the ratio of theoreticalstoichiometric oxygen flow to actual oxygen flow. For an oxidant that is100% oxygen, the oxygen flow equals the oxidant flow. For an oxidantthat an oxygen percentage X less than 100%, the oxygen flow in anoxidant stream is determined by dividing the oxidant flow rate by theoxygen percentage X; for example, to meet an oxygen requirement of 100SCFH using an oxidant containing 40% oxygen, 250 SCFH of the oxidant isrequired.

The following discussion pertains to the embodiment in which the firstfluid F1 is a fuel and the second fluid F2 and the third fluid F3 areboth oxidants. When a burner element 20 is in the passive state, theequivalence ratio is less than about 1, and is preferably at least about0.2. This signifies that a passive burner element 20 is operatingfuel-lean, with as much as five times the oxygen required for completecombustion. In contrast, when a burner element 20 is in the activestate, the equivalence ratio is greater than about 1, and is preferablyno more than about 10. This signifies that an active burner element 20is operating fuel-rich, with as little as 10% of the oxygen required forcomplete combustion.

A staging ratio is defined as the ratio of the amount of a reactantflowing through the staging nozzle 30 to the total amount of thatreactant flowing through the annular nozzles 24 and the staging nozzle30. For example, when the second fluid F2 and the third fluid F3 areoxidants, the staging ratio is the amount of oxygen provided by thestaging nozzle 30 divided by the total amount of oxygen provided by thestaging nozzle 30 and the annular nozzles 24 combined. If the secondfluid F2 and the third fluid F3 are the same fluids (i.e., with the sameoxygen concentration), then the staging ratio is simply the third fluidF3 flow rate divided by the sum of the second fluid F2 flow rate and thethird fluid F3 flow rate. But if the second fluid F2 and the third fluidF3 are different fluids (i.e., with different oxygen concentrations X2and X3, respectively), then the staging ratio is calculated to take intoaccount the concentration differences, as X₃F₃/(X₂F₂+X₃F₃), as would beunderstood by a person of skill in the art.

The burner 10 is preferably operated with a staging ratio of equal to orless than about 75%. For example, when oxidant is staged, i.e., when thesecond fluid F2 and the third fluid F3 are oxidants, at least about 25%of the oxygen to the burner 10 is flowed through the annular nozzles 24and no more than about 75% of the oxygen is flowed through the stagingnozzle 30. More preferably, the burner 10 is operated with a stagingratio of equal or less than about 40%. Further, as discussed above,because of the active or passive operation of each of the burnerelements 20, the one or more burner elements 20 active at one timeoperate with an excess of the first fluid F1 compared to stoichiometric,and the one or more burner elements 20 that are passive at the same timeoperate with an excess of the second fluid F2 compared tostoichiometric, thereby providing some amount of staging even withouttaking into account the third fluid F3 provided by the staging nozzle30.

The first fluid F1 exiting an active distribution nozzle 22 has anactive jet velocity determined by the first fluid F1 flow rate and thecross-sectional area of the distribution nozzle 22. The second fluid F2exiting an annular nozzle 24 has an annular jet velocity determined bythe second fluid F2 flow rate and the cross-sectional area of theannular nozzle 24. Similarly, the third fluid F3 exiting the stagingnozzle 30 has a staging jet velocity determined by the third fluid F3flow rate and the cross-sectional area of the staging nozzle 30. Theactive jet velocity preferably is greater than the annular jet velocity.In addition, for optimal performance of the burner 10, the staging jetvelocity should be less than or equal to the active jet velocity, andgreater than or equal to about 0.05 times the active jet velocity. Inone embodiment, the ratio of the staging jet velocity to the active jetvelocity is less than or equal to about 0.4. In another embodiment, theratio of the staging jet velocity to the active jet velocity is greaterthan or equal to about 0.1.

In one exemplary embodiment tested in a vertical firing arrangement(roof mounted), the first fluid F1 jet velocity through an activedistribution nozzle 22 was at least about 250 ft/s and was preferably atleast about 300 ft/s, and the velocity through a passive distributionnozzle 22 was about 20% of the active jet velocity. For a horizontalfiring arrangement, the active jet velocity can be considerably lowersince there is less need to combat buoyancy effects to avoid burnerblock overheating.

All of the control valves 23, 26, 28, and 32 are connected to andcontrolled by a controller 100 that is specifically programmed orconfigured to operate the burner 10. The controller 100 may includeconventional electronics components such as a CPU, RAM, ROM, I/Odevices, and the programming or configuration of the controller 100 maybe accomplished by a combination of one or more of hardware, firmware,software, and any other mechanism now known or later developed forprogramming operating instructions into a controller.

As described above, at least one of the fluids F1, F2, and F3 must be orcontain a fuel, and at least one of the fluids F1, F2, and F3 must be anoxidant or contain oxygen. The fuel can be a gaseous fuel, a liquidfuel, or a pulverized solid fuel in a gaseous carrier. In oneembodiment, F1 is a fuel and F2 and F3 are oxidants. In this case, F2and F3 may be the same oxidant, or F2 and F3 may be different oxidants.For example, in one preferred embodiment, F1 is a gaseous fuel such asnatural gas, F2 is an oxidant having an oxygen concentration of equal toor greater than about 70%, and F3 is an oxidant having an oxygenconcentration of equal to or greater than about 20.9%. In anothersimilar embodiment, F1 is a gaseous fuel such as natural gas, F2 is anoxidant having an oxygen concentration greater than that of air, and F3is air.

In an alternate embodiment, F1 is an oxidant and F2 and F3 are fuels. Inthis case F1 has an oxygen concentration equal to or greater than about26%, preferably equal to or greater than about 40%, and more preferablyequal to or greater than about 70%.

FIG. 3 shows one possible sequence of operation for the embodiment ofthe burner 10 illustrated in FIG. 1. For purposes of discussion, thefour burner elements 20 are labeled as a, b, c, and d. As shown, onlyone burner element 20 is active at a time, while the remaining burnerelements 20 are passive, and each burner element 20 is successivelyswitched to the active state when the previously active burner element20 is returned to the passive state.

In particular, in the depicted embodiment, burner element 20 a is activewhile burner elements 20 b, 20 c, and 20 d are passive. In other words,each of the annular nozzles 24 in each burner element 20 is receiving anapproximately equal flow of the second fluid F2, and only thedistribution nozzle 22 in burner element 20 a is receiving a higheractive flow of the first fluid F1, while the distribution nozzles 22 inthe other burner elements 20 b, 20 c, and 20 d are receiving a lowerpassive flow of the first fluid F1. This results in a relatively long,penetrating flame emanating from the active burner element 20 a andrelatively short (pilot) flames emanating from the passive burnerelements 20 b, 20 c, and 20 d. As further shown in the depictedembodiment, when burner element 20 b becomes active, burner element 20 areturns to the passive state and burner elements 20 c and 20 d remainpassive. Next, when burner element 20 c becomes active, burner element20 b returns to the passive state and burner elements 20 c and 20 aremain passive. Finally, when burner element 20 d becomes active, burnerelement 20 d returns to the passive state and burner elements 20 a and20 b remain passive.

The sequence shown in FIG. 3 and described above is only one ofessentially limitless variations. In one non-limiting example, oneburner element 20 is active at a time in a repeating sequence such asa-b-c-d or a-b-d-c or a-c-b-d or a-c-d-b. In another non-limitingexample, one burner element 20 is active at a time in a random sequence.In yet another non-limiting example, one burner element 20 is active ata time but each for either the same or different lengths of time.

Further, in other examples, more than one burner element 20 is active ata time. For example, for a burner 10 having three or more burnerelements 20, two burner elements 20 may be active and the remainderpassive. In general, for a burner 10 having n burner elements, anynumber of burner elements from 1 to n−1 may be active, and the remainderpassive.

Each burner element 20 can be switched from the passive to the activestate based on a preprogrammed time sequence, according to apredetermined algorithm, according to a random sequence, or depending onfurnace conditions. One or more sensors 110 may be positioned in thefurnace for sensing any parameter that may be relevant to determininglocations where more or less combustion heat is needed. For example, thesensor may be a temperature sensor, such that when the temperaturesensor is below a threshold setting, the burner element 20 oriented toheat the furnace in the region of that temperatures sensor may be madeactive more frequently or for longer periods of time. Or if atemperature sensor detects that a portion of the furnace or charge isreceiving insufficient heat, one or more burner elements 20 positionednear that portion of the furnace or angled toward that portion of thecharge can be switched to the active state, while burner elements 20 inportions of the furnace receiving excess heat can be switched to thepassive state.

Temperatures sensors may include contact sensors such as thermocouplesor RTDs located in the furnace walls, or non-contact sensors such asinfrared sensors, radiation sensors, optical sensors, cameras, colorsensors, or other sensors available to those in the industry. Othertypes of sensors may also be used to indicate the level of melting orheating in the furnace, including but not limited to proximity sensors(e.g., to sense the proximity of solid charge that has yet to melt) orconductivity sensors (e.g., to detect the higher conductivity of aliquid as compared to chunks of poorly interconnected solids).

Several benefits can be achieved by operation of the burner 10 asdescribed herein. Because heat can be preferentially directed to certainlocations and for longer or shorter periods of time, cold spots in thefurnace can be identified and eliminated, resulting in more uniformheating and melting. Particularly for vertical firing arrangements(i.e., roof-mounted burners pointing downward) as in FIG. 7, operatingthe burner with less than all of the burner elements 20 in active modereduces or eliminates the hazards of buoyant flames, thereby avoidingoverheating of the burner block and furnace roof. The fuel-richcombustion resulting from an active burner element 20, where the oxygenprovided through the annular nozzle 24 is significantly less than thestoichiometric oxygen required by the fuel provided through thedistribution nozzle 22, creates a non-oxidizing atmosphere near the meltbath to help protect the charge from undesirable oxidation.Additionally, activating the burner elements 20 in a repeated cyclicalpattern can b used to generate a vortex heating pattern that increasesresidence time of combustion gases, increases heat transfer rates, andimproves uniformity of heating, as shown for example in US2013/00954437. Further, selective activation of burner elements 20 andvariation of the staging ratio can be used to adjust the location ofmaximum heat flux emanating from the combustion reactions and to adjustflame coverage to accommodate various furnace geometries, conditions,and charge levels.

Various possible configurations of the burner include those shown inFIGS. 5A-5E. In an embodiment of the type shown in FIG. 5A, one or moreof the burner elements 20 may be angled radially outward at an angle αfrom the circle circumscribed by the burner elements 20, or from an axisdefined by the staging nozzle 30. Although the depicted embodiment showsall four burner elements 20 angled radially outward at the same angle α,it is understood that each burner element 20 may be angled at adifferent angle α_(n) depending on the furnace geometry and desiredoperating characteristics of the burner 10. The angle α may be equal toor greater than about 0° and is preferably equal to or less than about60°. More preferably, the angle α is at least about 10° and no greaterthan about 40°.

In an embodiment of the type shown in FIG. 5B, one or more burnerelements 20 may be angled tangentially to the circumscribed circle at anangle β to create swirl.

Although the depicted embodiment shows all four burner elements 20angled tangentially at the same angle β, it is understood that eachburner element 20 may be angled at a different angle β_(n) depending onthe furnace geometry and desired operating characteristics of the burner10. The angle β may be equal to or greater than about 0° and ispreferably equal to or less than about 60°. More preferably, the angle βis at least about 10° and no greater than about 40°.

In an embodiment of the type shown in FIG. 5C, a plurality of burnerelements 20 are positioned generally collinearly with each other todefine a line having a midpoint and ends. Although four burner elements20 are shown, this embodiment is applicable to a configuration with atleast two burner elements 20 and up to as many burner elements 20 as maybe required in a particular furnace. A staging nozzle 30 is positionedbetween each adjacent pair of burner elements 20, so that the burnerelements 20 and staging nozzles 30 alternate. For example, anarrangement with two burner elements 20 has one staging nozzle 30positioned between the two burner elements 20, and an arrangement withthree burner elements 20 has two staging nozzles 30 each positionedbetween a pair of adjacent burner elements 20. The burner elements 20may all be oriented perpendicularly to the burner face 14, or some orall of the burner elements 20 may be angled outward at an angle γ ofless than or equal to about 45° from the line midpoint toward one of theline ends. Similarly, the staging nozzles 30 may be orientedperpendicularly to the burner face 14, or some or all of the stagingnozzles 30 may be angled in one direction or the other along the line.In the depicted embodiment, a central staging nozzle 30 is orientedperpendicularly to the burner face 14, and a series of three collinearelements—a burner element 20, a staging nozzle 30, and another burnerelement 20—are positioned diametrically to either side and angled awayfrom the central staging nozzle 30 and toward their respective ends ofthe line.

In an embodiment of the type shown in FIG. 5D, a plurality of burnerelements 20 are positioned collinearly with each other to define a linehaving a midpoint and ends.

Although four burner elements 20 are shown, this configuration isapplication to a configuration with at least two burner elements 20 andup to as many burner elements 20 as may be required in a particularfurnace. An elongated or generally rectangular staging nozzle 30 havinga major axis at least 1.5 times as long as a minor axis is positionedadjacent to and spaced apart by a fixed distance from the burnerelements 20, with the major axis substantially parallel to the linedefined by the burner elements 20. The burner elements 20 may all beoriented perpendicularly to the burner face 14, or some or all of theburner elements 20 may be angled outward at an angle γ of less than orequal to about 45° from the line midpoint toward one of the line ends.

In an embodiment of the type shown in FIG. 5E, each burner element 20has a flat-flame configuration, wherein both the distribution nozzle 22and the annular nozzle 24 have an elongated or generally rectangularconfiguration having a major axis at least 1.5 times as long as a minoraxis. This type of flat flame burner is described in detail, for examplein U.S. Pat. No. 5,611,682. At least two staging nozzles 30 arepositioned adjacent to and spaced apart from the burner element 20, andare oriented generally collinearly to define a line that issubstantially parallel to the major axis of the burner element 20. Atleast two burner elements 20 are utilized in this configuration.

In any of the above-described configurations in FIGS. 5A-5E, a transientoperation scheme can be implemented similar to that describe above forthe configuration of FIG. 1. Specifically, at any given time, at leastone burner element 20 is operated in an active state, wherein the fluidflow through an active distribution nozzle 22 is greater than theaverage fluid flow through all of the distribution nozzles 22, while atleast one burner 20 is operated in the passive stage, wherein the fluidflow through a passive distribution nozzle 22 is less than the averagefluid flow through all of the distribution nozzles 22.

As shown in FIG. 7, one or more burners 10 may be mounted in the roof ofa furnace 200 (vertically installation) or in a sidewall of a furnace200 (horizontal installation). In a vertical installation, the burnerelements 20 are preferably arranged in a configuration such as in FIG.5A or FIG. 5B, to provide optimal heat flux to the charge whilepreventing overheating of the burner block. For example, as discussedabove, the burner elements 20 can be oriented to angle radially outwardfrom the circumscribed circle that encloses the staging nozzle 30 (FIG.5A). Alternatively, the burner elements 20 can be oriented in a vortexconfiguration (angled tangentially to the circumscribed circle) (FIG.5B). In a horizontal configuration, the burner elements 20 can bearranged in any array, and in particular may be arranged as in any ofFIGS. 5C-5E depending on the geometry of the furnace.

As shown in the data of FIG. 8, the burner 10 exhibits reduced NOxemissions compared with conventional oxy-fuel burners. Note that thescale of FIG. 8 is relative, normalized to the peak NOx of aconventional oxy-fuel burner. When the burner 10 is operated transientlyas described herein in a luminous mode (i.e., with a low shape factordistribution nozzle 22), the peak NOx emissions are only about 40% ofthat emitted by a conventional oxy-fuel burner. When the burner 10 isoperated transiently as described herein in a non-luminous mode (i.e.,with a high shape factor distribution nozzle 22), the peak NOx emissionsare even lower, only about 35% of that emitted by a conventionaloxy-fuel burner. In both cases, the burner 10 was operated with fuel asthe distributed fluid and oxidant as the staged fluid. Without beingbound by theory, this surprising result is thought to be a result of thehighly staged nature of the combustion produced by the burner 10, whichresults in a first fuel-rich flame zone that produces low NOx due tolimited oxygen availability, and a second fuel-lean flame zone thatproduces low NOx due to its low combustion temperatures.

The present invention is not to be limited in scope by the specificaspects or embodiments disclosed in the examples which are intended asillustrations of a few aspects of the invention and any embodiments thatare functionally equivalent are within the scope of this invention.Various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art andare intended to fall within the scope of the appended claims.

1. A transient heating burner comprising: at least two burner elementseach comprising: a distribution nozzle configured to flow a first fluid;and an annular nozzle surrounding the distribution nozzle and configuredto flow a second fluid; and a controller programmed: to independentlycontrol the flow of the first fluid to each distribution nozzle suchthat at least one of the distribution nozzles is active and at least oneof the distribution nozzles is passive, wherein flow in an activedistribution nozzle is greater than an average flow to the distributionnozzles and flow in a passive distribution nozzle is less than theaverage flow to the distribution nozzles; wherein the first fluidcontains a reactant that is one of fuel and oxidant and the second fluidcontains a reactant that is the other of fuel and oxidant.
 2. The burnerof claim 1, further comprising a sensor configured to provide a signalto the controller; wherein the controller is programmed to control eachdistribution nozzle to be active or passive based on the signal; whereinthe sensor is selected from the group consisting of temperature sensors,radiation sensors, optical sensors, cameras, color sensors, conductivitysensors, proximity sensors, and combinations thereof.
 3. The burner ofclaim 1, wherein the burner elements are spaced substantially evenlyapart in a circumscribed circle.
 4. The burner of claim 3, wherein atleast one of the burner elements is angled radially outward at an angleα from the circumscribed circle, wherein the angle α is less than orequal to 60°.
 5. The burner of claim 3, wherein at least one of theburner elements is angled tangentially at an angle β with respect to thecircumscribed circle, wherein the angle β is less than or equal to 60°.6. The burner of claim 1, wherein the controller is programmed tocontrol the first fluid flow to a passive distribution nozzle to begreater than zero and less than or equal to half the flow rate of anactive distribution nozzle.
 7. The burner of claim 1, further comprisingat least one staging nozzle configured to flow a third fluid; whereinthe third fluid contains the same reactant as the second fluid; andwherein the controller is further programmed to control a staging ratioto be less than or equal to 75%, wherein the staging ratio is the ratioof the reactant contained in the third fluid flow to the sum of thereactant contained in the second fluid flow and the third fluid flow. 8.The burner of claim 7, wherein the burner elements are spacedsubstantially evenly apart in a circumscribed circle; and wherein thestaging nozzle is positioned within the circumscribed circle.
 9. Theburner of claim 7, wherein the burner elements and the staging nozzleare positioned collinearly with each staging nozzle located equidistantbetween two burner elements.
 10. The burner of claim 7, wherein thedistribution nozzles and annular nozzles each have a cross-section witha minor axis and a major axis at least 1.5 times as long as the minoraxis; and wherein at least two staging nozzles are positionedcollinearly, and are adjacent to each burner element and substantiallyparallel to the major axes.
 11. The burner of claim 7, wherein thestaging nozzle has a cross-section with a minor axis and a major axis atleast 1.5 times as long as the minor axis; and wherein at least twoburner elements are positioned collinearly, and are adjacent to thestaging nozzle and substantially parallel to the major axis.
 12. Amethod of operating a burner in a furnace, the burner having at leasttwo burner elements each comprising a distribution nozzle surrounded byan annular nozzle, the method comprising: selecting at least one of thedistribution nozzles to be active and at least one of the distributionnozzles to be passive; flowing a first fluid at an active jet flow ratethrough the active distribution nozzles; flowing the first fluid at apassive jet flow rate through the passive distribution nozzles; andflowing a second fluid at a second fluid flow rate through each of theannular nozzles; wherein the active jet flow rate is greater than anaverage first fluid flow rate through the distribution nozzles and thepassive jet flow rate is less than the average first fluid flow ratethrough the distribution nozzles; and wherein the first fluid contains areactant that is one of fuel and oxidant and the second fluid contains areactant that is the other of fuel and oxidant.
 13. The method of claim12, further comprising: sensing a parameter in the furnace; reselectingwhich distribution nozzles are active and which distribution nozzles arepassive based on the sensed parameter; and periodically repeating thesensing and reselecting steps.
 14. The method of claim 12, wherein theratio of the active jet flow rate to the passive jet flow rate is from 5to
 40. 15. The method of claim 12, wherein a burner element having apassive distribution nozzle has an equivalence ratio of from 0.2 to 1,and a burner element having an active distribution nozzle has anequivalence ratio of from 1 to 10; and wherein the equivalence ratio isthe ratio of theoretical stoichiometric oxidant flow through one of thedistribution nozzle and the annular nozzle to actual oxidant flowthrough the one of the distribution nozzle and the annular nozzle tocombust the fuel flowing through the other of the distribution nozzleand the annular nozzle.
 16. The method of claim 12, the burner furtherhaving at least one staging nozzle, the method further comprising:flowing a third fluid through the staging nozzle, wherein third fluidcontains the same reactant as the second fluid.
 17. The method of claim16, wherein a staging ratio is the ratio of the reactant contained inthe third fluid flowing through the staging nozzle to the sum of thereactant contained in the third fluid flowing through the staging nozzleand reactant contained in the second fluid flowing through the annularnozzles; and wherein the staging ratio is less than or equal to 40%. 18.The method of claim 16, wherein fuel exiting an active distributionnozzle has an active jet velocity and oxidant exiting the staging nozzlehas a staging jet velocity; and wherein the ratio of the staging jetvelocity to the active jet velocity to be at least 0.05 and less than 1.